Development of a Greener Hydroformylation Process Guided by Quantitative Sustainability Assessments

Environmental impacts and economics associated with a potentially greener, Rh-catalyzed, 1-octene hydroformylation process in CO₂-expanded liquid (CXL) medium are quantitatively assessed against a conventional Co-catalyzed process. The economic analysis shows a more than 30% lower capital investment for the CXL process compared to the conventional Co-catalyzed process of similar capacity. This is due to the higher reaction and catalyst recovery efficiencies at milder reaction temperature and pressures (compared to the conventional process) used in the CXL process. The total production cost (TPC) associated with the CXL process is lower than the conventional process when the Rh makeup rate is lower than 0.94% (of the total amount of Rh in the reactor) per hour at the current Rh price ($20,800/lb). This translates to an economic viability criterion of ($makeup Rh/$TPC) being 0.042 or less. Life cycle analysis (LCA) was performed using GaBi software and an EIO-LCA method based on plant scale simulation of both the conventional and continuous CXL processes to produce 150 kton/year of nonanal. Gate-to-gate LCA projections show that the CXL process is environmentally friendlier than the conventional process in most impact categories such as ecotoxicity, greenhouse gas emissions, and smog formation. Predicted emissions for the conventional process are of the same order of magnitude as those reported from an actual plant of similar capacity. Cradle-to-gate environmental impacts are 1 to 2 orders of magnitude greater than the gate-to-gate impacts with energy usage for the production of raw materials being the major source of adverse environmental impacts. The EIO-LCA results agree with the GaBi analysis. Our results show that the environmental performance of the CXL process can be further improved with lower solvent usage, thus also providing valuable guidance for process optimization

<i>110th Anniversary:</i> Near-Total Epoxidation Selectivity and Hydrogen Peroxide Utilization with Nb-EISA Catalysts for Propylene Epoxidation

The Nb-EISA catalyst with relatively low Nb loadings (∼2 wt %) shows exceptional propylene epoxidation performance with H2O2 as oxidant at 30–40 °C, 5–9 bar propylene pressure with nearly total propylene oxide (PO) selectivity (>99%), H2O2 utilization (>99%) toward PO formation, high productivity (∼3200 mg/h/g), and mild Nb leaching (3–6%). The predominantly Lewis acidic nature of the Nb-EISA catalysts favors epoxidation while their relatively low Brønsted acidity inhibits H2O2 decomposition and Nb leaching. At higher Nb loadings (8–17 wt %), the catalytic performance deteriorates. However, significant performance improvements were achieved when the Nb-EISA materials are calcined in N2 (instead of air) during synthesis, depositing a carbon layer in the pores. The resulting pore hydrophobicity not only inhibits epoxide ring opening but also increases propylene concentration inside the pores resulting in higher EO productivity and lower H2O2 decomposition. The carbonized Nb-EISA materials also show improved stability to leaching

Facile Ozonation of Light Alkanes to Oxygenates with High Atom Economy in Tunable Condensed Phase at Ambient Temperature

We have demonstrated the oxidation of mixed alkanes (propane, n-butane, and isobutane) by ozone in a condensed phase at ambient temperature and mild pressures (up to 1.3 MPa). Oxygenated products such as alcohols and ketones are formed with a combined molar selectivity of >90%. The ozone and dioxygen partial pressures are controlled such that the gas phase is always outside the flammability envelope. Because the alkane–ozone reaction predominantly occurs in the condensed phase, we are able to harness the unique tunability of ozone concentrations in hydrocarbon-rich liquid phases for facile activation of the light alkanes while also avoiding over-oxidation of the products. Further, adding isobutane and water to the mixed alkane feed significantly enhances ozone utilization and the oxygenate yields. The ability to tune the composition of the condensed media by incorporating liquid additives to direct selectivity is a key to achieving high carbon atom economy, which cannot be achieved in gas-phase ozonations. Even in the liquid phase, without added isobutane and water, combustion products dominate during neat propane ozonation, with CO2 selectivity being >60%. In contrast, ozonation of a propane+isobutane+water mixture suppresses CO2 formation to 15% and nearly doubles the yield of isopropanol. A kinetic model based on the formation of a hydrotrioxide intermediate can adequately explain the yields of the observed isobutane ozonation products. Estimated rate constants for the formation of oxygenates suggest that the demonstrated concept has promise for facile and atom-economic conversion of natural gas liquids to valuable oxygenates and broader applications associated with C–H functionalization

Aqueous Phase Hydrogenation of Acetic Acid and Its Promotional Effect on <i>p</i>‑Cresol Hydrodeoxygenation

A systematic study of the comparative performances of various supported noble metal catalysts for the aqueous phase hydrogenation of acetic acid (as a model carboxylic acid in bio-oils) by itself and in combination with <i>p</i>-cresol (as a model phenolic compound in bio-oils) is presented. It was found that Ru/C catalyst shows the highest activity for acetic acid hydrogenation among the tested catalysts, followed by Ru/Al₂O₃, Pt/C, Pt/Al₂O₃, Pd/Al₂O₃, and Pd/C. CH₄ and CO₂ were observed to be the major products on all of these catalysts at typical hydroprocessing temperatures (∼300 °C). A systematic study on parametric effects with the Ru/C catalyst shows that the product distribution is dependent upon the temperature and presence of water. At low temperatures (∼150 °C), acetic acid hydrogenation is favored with higher selectivity to ethanol, while at high temperatures (∼300 °C), acetic acid decomposition and ethanol reforming/hydrogenolysis dominate with CO₂ and CH₄ as the major products. When water is replaced with <i>n</i>-heptane at otherwise similar conditions, the esterification reaction is favored over ethanol reforming/hydrogenolysis, resulting in substantial formation of ethyl acetate. With a mixed feed of acetic acid and <i>p</i>-cresol over the Ru/C catalyst, acetic acid hydrogenation is suppressed and <i>p</i>-cresol hydrodeoxygenation is favored, as inferred from the observed high selectivity to methylcyclohexane

Expectations for Manuscripts Contributing to the Field of Solvents in ACS Sustainable Chemistry & Engineering

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Liquid-Phase Oxidation of Ethylene Glycol on Pt and Pt–Fe Catalysts for the Production of Glycolic Acid: Remarkable Bimetallic Effect and Reaction Mechanism

A highly active and selective Pt–Fe alloy catalyst on CeO2 support is reported in this work for aqueous phase oxidation of ethylene glycol (EG) to glycolic acid. The Pt–Fe nanoparticles are highly alloyed with a face-centered cubic (fcc) type of crystal structure and a chemical state of Pt0/Fe0, as confirmed from X-ray diffraction and extended X-ray absorption fine structure characterizations, respectively. Compared to the monometallic Pt catalyst, the Pt–Fe catalyst shows more than a 17-fold higher initial TOF, while achieving complete EG conversion in 4 h at 70 °C and ambient O2 pressure under alkaline conditions. The synergistic bimetallic effect occurs due to significantly changing the O2 adsorption-dissociation characteristics on the catalyst surface. The addition of a base shows a promotional effect on both Pt and Pt–Fe catalysts at low NaOH concentrations but an inhibition effect is observed for both catalysts at sufficiently high NaOH concentrations. Furthermore, the base enhances the synergistic effect observed with Pt–Fe catalyst

Correlation between Lignin–Carbohydrate Complex Content in Grass Lignins and Phenolic Aldehyde Production by Rapid Spray Ozonolysis

We provide strong evidence that the amounts of phenolic aldehydes (vanillin and p-hydroxybenzaldehyde, pHB) selectively released during rapid ozonolysis of grass lignins are correlated with the unsubstituted aryl carbons of lignin–carbohydrate complexes present in these lignins. In the case of acetosolv lignin from corn stover, we observed a steady yield of vanillin and pHB (cumulatively ∼5 wt % of the initial lignin). We demonstrate the continuous ozonolysis of the lignin in a spray reactor at ambient temperature and pressure. In sharp contrast, similar ozonolysis of acetosolv lignin from corn cobs resulted in a twofold increase in the combined yield (∼10 wt %) of vanillin and pHB. Structural analysis with 1H–13C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance revealed that signals assigned to unsubstituted aryl carbons of lignin–carbohydrate complexes are quantitatively correlated to phenolic aldehyde production from spray ozonolysis. The ratios of the integrated peak volumes corresponding to coumarates and ferulates in the HSQC spectra of cob and corn stover lignins (SLs) are 2.4 and 2.0, respectively. These ratios are nearly identical to the observed 2.3-fold increase in pHB and 1.8-fold increase in vanillin production rates from corn cob lignin compared to corn SL. Considering that the annual U.S. lignin capacity from these grass lignin sources is ∼60 million MT, the value creation potential from these flavoring agents is conservatively ∼$50 million annually from just 10% of the lignin. These new insights into structure/product correlation and spray reactor characteristics provide rational guidance for developing viable technologies to valorize grass lignins

Guaiacol Hydrodeoxygenation and Hydrogenation over Bimetallic Pt‑M (Nb, W, Zr)/KIT‑6 Catalysts with Tunable Acidity

Owing to a high oxygen content, bio-oils from the fast pyrolysis of biomass require upgrading to meet fuel specification standards. Catalytic hydrodeoxygenation (HDO) of bio-oils faces several challenges such as low hydrocarbon yields, the requirement of high H2 partial pressure for complete deoxygenation, and catalyst deactivation caused by coking/carbon deposition. In the present work, Pt supported on Nb, W, and Zr-incorporated KIT-6 materials were prepared, characterized, and tested for the gas-phase HDO of guaiacol, a widely used model compound of bio-oil. Facile HDO of guaiacol was observed over a 1 wt % Pt/Nb-KIT-6 catalyst, with ∼90% conversion and ∼75% hydrocarbon selectivity under relatively mild hydrogen partial pressure (0.5 MPa) at 400 °C and 33 h–1 weight hourly space velocity (WHSV). No significant catalyst deactivation was observed during a 24-h continuous run indicating that the mesoporous support provides enhanced coking resistance. Mechanistic investigations indicate that the tunable acidity of the supports promotes transalkylation reactions, which favor increased aromatic hydrocarbon yields. A plausible reaction mechanism is postulated based on correlating the number of metal and acid sites with the measured rates for the individual reaction steps